1. Field of the Invention
The present invention relates to radio frequency (RF) communications, and more particularly, to an RFID transponder having an active amplifier that receives a signal, and then amplifies and re-transmits the received signal on the same frequency.
2. Description of Related Art
Wireless communication systems that communicate signals over the RF spectrum are well known in the art. Such systems have numerous diverse applications, including cordless and cellular telephones, paging, wireless computer networks, mobile radio for police, fire and municipal services, remote control devices for garage doors and other devices, and remote data sensing, to name just a few. A drawback of all such communication systems is that the radiated power becomes attenuated over distance. Accordingly, it is known to introduce one or more amplifier units between a source and destination of an RF signal, known as repeaters. Such repeater stations amplify and retransmit a received signal in order to make up for the power loss between the source and destination. Repeater systems are advantageous for many applications, but nevertheless add cost and complexity to a communication system that would be unacceptable for many applications. Another drawback is that it is necessary to maintain isolation between receiving and transmitting antennas of the repeater system in order to avoid interference between the received and transmitted signals.
One wireless communication application that is particularly sensitive to such range limitations and the drawbacks of conventional repeaters is radio frequency identification (RFID) technology. In the automatic data identification industry, the use of RFID transponders (also known as RFID tags) has grown in prominence as a way to track data regarding an object to which the RFID transponder is affixed. An RFID transponder generally includes a semiconductor memory in which digital information may be stored, such as an electrically erasable, programmable read-only memory (EEPROMs) or similar electronic memory device. Under a technique referred to as “backscatter modulation,” the RFID transponders transmit stored data by reflecting varying amounts of an electromagnetic field provided by an RFID interrogator by modifying their antenna matching impedances.
The RFID transponders may either extract their power from the electromagnetic field provided by the interrogator, or alternatively, may include their own power source. RFID transponders that include a power source are particularly advantageous in applications in which maximum range is desired, such as in remote vehicle toll collection and transportation monitoring. Notwithstanding this performance advantage of battery-powered RFID transponders over field-powered RFID transponders, there is a continuing demand to further increase the range at which such RFID transponders can communicate without having to make associated increases in size, weight and cost of the RFID transponders. Accordingly, it would be very desirable to provide a method for increasing the effective range of an RFID transponder as well as for other types of RF communication systems without increasing the size, weight or cost of the transponder.